/*reset css*/
*{margin: 0; padding: 0;box-sizing: border-box;}
*::after,*::before{box-sizing: border-box;}
ul,ol{list-style: none;}

/*global css*/
body{
    overflow: hidden;
}
body>.page{
    display: flex;
    flex-wrap: wrap;
}

body>.page section{
    border: 1px solid green;
    width: 50vw;
    height: 50vh;
}

/*app2 css*/
#app2 .tab-bar{
    border: 1px solid black;
    display: flex;
}
#app2 .tab-bar li{
    width: 50%;
    border: 1px solid black;
}

#app2 .tab-content>li{
    display: none;
}
#app2 .tab-bar>li.selected{
    background-color: pink;
}

#app2 .tab-content>li.active{
    display: block;
}

/*app3 css*/
#app3 .square{
    border: 1px solid  red;
    width: 10vw;
    height: 10vw;
    margin-top: 3vw;
    margin-left: 3vw;
    transition: transform 1s;
}

#app3 .square.active{
    transform: translateX(10vw);
}

/*app4 css*/
#app4 .circle{
    border: 1px solid black;
    margin-top: 3vw;
    margin-left: 3vw;
    width: 10vw;
    height: 10vw;
    border-radius: 50%;
}

@keyframes change{
    0%{
        background-color: pink;
    }
    100%{
        background-color: blueviolet;
    }
}

#app4 .circle.active{
    animation: change 1s linear infinite alternate;
}
